Silicon-carbon composite materials and methods
The invention provides methods for providing composite particles with a carbon coating and the resulting core-shell particulate material. The process comprises subjecting a plurality of precursor composite particles to a heat treatment in contact with a pyrolytic carbon precursor such that an outer shell of a pyrolytic conductive carbon material is formed on the precursor composite particles, wherein the heat treatment is carried out at a temperature of no more than 700° C.
1 . A process for preparing core-shell composite particles, the process comprising:
(a) providing a plurality of precursor composite particles comprising:
i. a porous carbon framework comprising micropores and/or mesopores, wherein the total pore volume of micropores and mesopores is at least 0.4 cm 3 /g, and wherein the PD 50 pore diameter of the porous carbon framework is no more than 10 nm;
wherein the total pore volume of micropores and mesopores and the PD 50 pore diameter of the porous carbon framework are measured by nitrogen gas absorption at 77 K down to a 15 relative pressure p/p 0 of 10 −6 using QSDFT in accordance with ISO 15901-2 and ISO 15901-3; and
ii. a plurality of nanoscale silicon domains disposed with the porous carbon framework;
(b) subjecting the plurality of precursor composite particles to a heat treatment in contact with a pyrolytic carbon precursor such that an outer shell of a pyrolytic conductive carbon material is formed on the precursor composite particles, wherein the heat treatment is carried out at a temperature of no more than 680° C.;
wherein the step (a) of providing a plurality of precursor composite particles comprises contacting a silicon precursor gas with a plurality of porous carbon particles at a temperature of between 200 and 500° C.
2 . A process according to claim 1 , wherein the heat treatment in step (b) is carried out at a temperature of no more than 650° C.
3 . A process according to claim 1 , wherein the heat treatment is carried out at a temperature of at least 500° C.
4 . A process according to claim 1 , wherein the pyrolytic carbon precursor is contacted with the composite particles as a vapour.
5 . A process according to claim 4 , wherein the pyrolytic carbon precursor is selected from polyaromatic hydrocarbons comprising from 10 to 25 carbon atoms and optionally from 1 to 3 heteroatoms, bicyclic monoterpenoids; and C 2 -C 10 hydrocarbons.
6 . A process according to claim 5 , wherein the pyrolytic carbon precursor is selected from
(i) naphthalene, anthracene, tetracene, pentacene, fluorene, acenapthene, phenanthrene, fluoranthrene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone and alkyl-substituted derivatives thereof,
(ii) camphor, borneol, eucalyptol, camphene, careen, sabinene, thujene and pinene; and
(iii) methane, ethylene, propylene and acetylene.
7 . A process according to claim 1 , wherein the pyrolytic carbon precursor vapour is contacted with a transition metal catalyst at a temperature of at least 500° C. prior to contact with the composite particles.
8 . A process according to claim 7 , wherein the transition metal catalyst comprises nickel, iron, cobalt, copper and mixtures thereof.
9 . A process according to claim 7 , wherein the transition metal catalyst is disposed on the surface of the composite particles.
10 . A process according to claim 7 , wherein gaseous nickel carbonyl is thermally decomposed to deposit nickel onto the surface of the composite particles prior to step (b).
11 . A process according to claim 10 , wherein the carbon-coated particulate material is contacted with carbon monoxide gas after step (b) to form gaseous nickel carbonyl, thereby removing nickel from the carbon-coated composite particles.
12 . A process according to claim 1 , wherein step (b) comprises contacting the composite particles with a solution or dispersion of a pyrolytic carbon precursor in a solvent, and removing the solvent to provide composite particles coated with the pyrolytic carbon precursor, prior to the heat treatment.
13 . A process according to claim 12 , wherein the pyrolytic carbon precursor is a polymer or oligomer comprising a carbon-containing backbone.
14 . A process according to claim 1 , wherein the outer shell of pyrolytic conductive carbon material has a thickness of no more than 10 nm.
15 . A process according to claim 1 , wherein
the total pore volume of micropores and mesopores of the porous carbon framework as measured by gas adsorption is at least 0.45 cm 3 /g and no more than 2.2 cm 3 /g;
the PD 50 so pore diameter of the porous carbon framework is no more than 8 nm;
the precursor composite particles have a D 50 particle diameter of at least 1 μm and no more than 50 μm.
16 . A process according to claim 1 , wherein the electroactive material is silicon.
17 . A process according to claim 1 , wherein the duration of the heat treatment in step (b) is from 1 to 3 hours.
18 . A particulate material consisting of a plurality of core-shell composite particles obtainable by a process according to claim 1 .
19 . A process for preparing core-shell composite particles, the process comprising:
(a) providing a plurality of precursor composite particles comprising:
i. a porous carbon framework comprising micropores and/or mesopores, wherein a total pore volume of micropores and mesopores is at least 0.4 cm 3 /g, and wherein a PD 50 pore diameter of the porous carbon framework is no more than 10 nm;
ii. a plurality of nanoscale silicon domains disposed with the porous carbon framework;
(b) subjecting the plurality of precursor composite particles to a heat treatment in contact with a pyrolytic carbon precursor vapor such that an outer shell of a pyrolytic conductive carbon material is formed on the plurality of precursor composite particles, wherein the heat treatment is carried out at a temperature of no more than 680° C.;
wherein the pyrolytic carbon precursor vapor is contacted with a transition metal catalyst at a temperature of at least 500° C. prior to contact with the plurality of precursor composite particles.
20 . A process according to claim 19 , wherein the transition metal catalyst comprises nickel, iron, cobalt, copper and mixtures thereof.
21 . A process according to claim 19 , wherein the transition metal catalyst is disposed on a surface of the composite particles.
22 . A process according to claim 19 , wherein gaseous nickel carbonyl is thermally decomposed to deposit nickel onto a surface of the composite particles prior to step (b).
23 . A process according to claim 22 , wherein the carbon-coated particulate material is contacted with carbon monoxide gas after step (b) to form gaseous nickel carbonyl, thereby removing nickel from the carbon-coated composite particles.